Constant stress pin tip for testing integrated circuit chips

ABSTRACT

A structure and method of constructing a tip for a contact pin used in IC test housing for testing integrated circuits. As the pin is deflected when the device under test (DUT) pad engaged the tip of the pin, the tip pressure normally increases as the elastomers biasing the pin are engaged. This causes uneven pressure on the tip and will create debris and reduce tip life. By making the surface of the tip wider in the X or Y direction the surface pressure is reduced during the pin contact cycle. It is also possible to reduce tip pressure by having the top surface change in the Z axis so that recedes downwardly along its travel path, the pressure is reduced.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from issued U.S. Pat. No. 7,639,026;issued U.S. Pat. No. 6,854,981, issued U.S. Pat. No. 7,445,465, issuedU.S. Pat. No. 7,059,866; issued U.S. Pat. No. 7,737,708 and USPublication No. 2006/0216962 and all of common ownership and further areall hereby incorporated by reference along with all applications fromwhich they claim priority.

FIELD OF THE DISCLOSURE

The present invention is directed to devices for testing of integratedcircuit chips or dice from IC wafers. More narrowly, however, thedisclosure deals with test contacts for interfacing pads or leads of adevice to be tested with corresponding pads of a device under test(DUT). In addition, improvements in the pin contact tip and shape of thepin as a whole which contacts the DUT during test are disclosed.

BACKGROUND

The testing of integrated circuit devices is performed to ensure thatsuch devices, when sold to a customer, are of as high a degree ofquality as possible. Various types of test apparatus have been utilizedover the years to accomplish testing. Typically, a tester includes aprinted circuit board which has defined thereon a plurality ofconductive traces. These traces on the circuit board, or load board, areassociated with corresponding functions of the test apparatus.

In order to accomplish testing, it is necessary to interconnect a lead,in the case of a leaded device under test, or a pad, of a nonleadeddevice under test, to a corresponding trace on the load board. A testset or test socket having a plurality of contacts is interposed betweenthe device under test and the load board in order to effectuateinterconnection. A contact is engaged, at an upper end thereof, by thelead or pad of the DUT, depending upon the type of DUT being tested,with its corresponding trace on the load board. A lower end of thecontact is in engagement with a trace on the load board.

As technology has progressed, the size, shape and electronic propertiesof contacts have evolved in response to the construction of test setsand load boards and the architecture of devices to be tested. At onetime, it was considered necessary to have a wiping action at the variouslocations of engagement of the contact ends by the lead or pad of theDUT and the pad on the load board. Such wiping action was deemed tofacilitate a good transmission path through the contact because of agood connection at either end thereof. It has become more apparent,however, that the measure of wiping action formerly considered necessaryto maintain a good transmission path need not be of a degree as wasformerly believed. Further, it has been recognized that excessive wipingaction can damage component parts at the various points of engagement ofthe contact, and thereby significantly decrease the life of the testsocket and tester load board. Consequently, various attempts have beenmade to minimize abrading of one surface relative to another. Variouselastomeric mounting means have been devised in an effort to minimizeabrasion and consequent deterioration of components.

Another problem which has been discovered is the diminishment ofeffectiveness of testing as a result of the employment of matte tin onleads and pads of various types of DUTs. Such a material is applied toDUT components which facilitate soldering to an ultimate host circuitboard. Because of its softness, however, such materials are often shedas debris which can fall into the test housing and disrupt the testing.

It is to these dictates and shortcomings of the prior art that thepresent disclosure is directed. The present invention is a contacthaving a structure which minimizes tin buildup on the contact.

BRIEF SUMMARY

To assist the reader in preparing to digest the detailed description andclaims below, a short summary has been provided. It is far from completeand only provides a glimpse of the invention concepts. It is notintended to define the scope of the invention. The claims perform thatfunction

Disclosed is a method of reducing tip pressure between a device undertest (DUT) and a test pin in a test housing, the pin having a tip whichhas a contact surface comprising:

a. forming the tip of the pin so that it has a curvature on its contactsurfaces, so that when it engages a contact of a DUT, the area ofcontact between the tip and DUT travels along the curved tip surface;

b. forming a widening the tip contact surface from a point of initialcontact with the DUT to a point of final contact with the DUT as it isinserted into the housing, where the tip contact surface is wider towardthe point of final contact.

Also disclosed is a method of reducing tip pressure between a deviceunder test (DUT) and a test pin in a test housing, the pin having a tipwhich has a contact surface comprising:

a. forming the tip of the pin so that it has a curvature on its contactsurfaces, so that when it engages a contact of a DUT, the area ofcontact between the tip and DUT travels along the curved tip surface;

b. forming a declining tip height along the tip contact surface from apoint of initial contact with the DUT to a point of final contact withthe DUT as it is inserted into the housing, where the tip height islower toward the point of final contact.

1. A controlled pressure test pin for use in a test pin housing on adevice under test (DUT) the pin comprising:

a. a tip formed at an end of the test pin, the tip being configured toengage a contact on the DUT from an initial point where the tip firstengages the DUT to a final point where the DUT is in a test position inthe housing, during which the pin is deflected into the housing, b. saidtip having a top surface configured to engage the DUT, said top surfacebeing narrower at the point of initial engagement than at said finalpoint, so that pressure between the tip and the DUT will tend to be moreconstant instead of rising as tip deflection increases.

Also disclosed is a controlled pressure test pin for use in a test pinhousing on a device under test (DUT) the pin comprising:

a. a tip formed at an end of the test pin, the tip being configured toengage a contact on the DUT from an initial point where the tip firstengages the DUT to a final point where the DUT is in a test position inthe housing, during which the pin is deflected into the housing,

b. said tip having a top surface configured to engage the DUT, said topsurface being higher at the point of initial engagement than at saidfinal point so that pressure between the tip and the DUT will tend to bemore constant instead of rising as tip deflection increases.

Also disclosed is a controlled pressure test pin for use in a test pinhousing on a device under test (DUT) the pin comprising:

a. a tip formed at an end of the test pin, the tip being configured toengage a contact on the DUT from an initial point where the tip firstengages the DUT to a final point where the DUT is in a test position inthe housing, during which the pin is deflected into the housing,

b. said tip having a top surface configured to engage the DUT, said topsurface being higher at the point of initial engagement than at saidfinal point so that pressure between the tip and the DUT will tend to bemore constant instead of rising as tip deflection increases; and

c. said tip having a top surface configured to engage the DUT, said topsurface being higher at the point of initial engagement than at saidfinal point so that pressure between the tip and the DUT will tend to bemore constant instead of rising as tip deflection increases.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a side plan schematic view of a test pin.

FIG. 2 is top plan view of the embodiment in FIG. 1.

FIG. 3 is close up end view of the embodiment in FIG. 1.

FIG. 4 is a top perspective view of a second embodiment of a test pin.

FIG. 5 is a close up perspective view of the tip of the test pin in FIG.4.

FIG. 6 is a side view of the tip in multiple positions.

FIG. 7 is a close up end view of the pin in FIG. 4.

FIG. 8 is a side plan view of a third embodiment of a test pin.

FIG. 9 is an end view of the pin in FIG. 8.

FIG. 10 is a close up top view of the pin in FIG. 8.

FIG. 11 is a perspective view of a fourth embodiment of a test pin.

FIG. 11a is a close up view taken from circle A of FIG. 11.

DETAILED DESCRIPTION

This disclosure details a test contact pin for use in a housing intendedprimarily to test integrated circuit chips or dice (aka device undertest—DUT).

Prior art test pins necessarily apply an uneven contact force on DUTpads or leads when the DUT is loaded to test a invention provides asconstant a stress as possible between the contact tip and the DUT padover the life of the contact and as constant a stress as possible duringthe actuation of the contact. This invention also extends the operatingrange of the contact by allowing the contact tip to wear a greaterdistance without falling below a specified pressure.

As constant a stress as possible during the actuation of the contact isaccomplished by tapering the tip of the contact in the X-Y direction. Atthe beginning of the actuation, the force is low and the width of thetip is narrow. Low force on a narrow tip creates a controllable stressat the beginning of the actuation. At the end to the actuation, theforce is higher and the width of the tip is wider. High force on a widertip creates a controllable stress at the end of the actuation. Bycontrolling the changing force during the actuation of the contact andby controlling the changing width of the contact tip during theactuation, a more consistent stress between the contact tip and the DUTpad is achieved during the actuation of the contact.

As constant a stress as possible over the life of the contact isaccomplished by tapering the tip of the contact in the Z direction. Atthe beginning of the life of the contact, tip wear is at its minimum,the contact tip is wide and the contact is able to be actuated to itsfully compressed position causing the force to be at its maximum value.High force on a wider tip creates a controllable stress at the beginningof the life of the contact. At the end of the life of the contact, tipwear is at its maximum, the contact tip is narrow and the contact isunable to be actuated to its fully compressed position causing the forceto be at its minimum value. Low force on a narrow tip creates acontrollable stress at the end of the life of the contact. Bycontrolling the changing force during the life of the contact and bycontrolling the changing width of the contact tip during the life, amore consistent stress between the contact tip and the DUT pad isachieved during the life of the contact.

By controlling the contact tip taper in both the Z and X-Y directions atthe same time, a more consistent stress between the contact tip and DUTpad can be achieved during the actuation of the contact and over thelife of the contact.

See attached “Pressure vs Wear” graph to see how the 11.8 degree taperextends the operating range from 0.0675 mm wear to 0.1175 mm of contacttip wear.

There are various combinations of tapers possible. A) The contact tiptaper in the Z direction. B) The contact tip taper in the X or Y or bothdirections; C) The contact simultaneous tip tapers in both the Z and Xor Y or both X and Y directions.

FIGS. 1-3 illustrate a pin 10 having a tip 12. The operation of the pinin the housing (not shown) is known from cited references referred toand incorporated in, this document.

Just below the tip 12 is a tip neck 14 which may be a constructedportion as shown or the same thickness as the body of the pin.

Rising from the neck are 2 pairs of opposing sidewalls 20 a-20 b and 20c-20 d. The walls may also be curved or form a cylinder. For simplicitythe sidewalls 20 a-20 b will be designated the X direction, 20 c-d the Ydirection, and top surface 22 in the Z direction.

Top surface 22 is cylindrical or hemispherical depending on whether thestress relief is in the x, y, z axis or some or all of them.

Notice that the edge 22 c of surface 22 (adjacent sidewall 20 c, willencounter the DUT test pad first on insertion. As the pin is deflecteddownwardly into the housing, the DUT pad will move along the surface 22toward edge 22 d. As the pin is deflected downwardly, the pressure onthe tip is increased, because of the compression of resilient members(not shown) which bias the pin toward the DUT.

To reduce the pressure, one of the following design options on the tipmay be employed:

1. The width of the tip from 22 c to 22 d is progressively widened sothat the pressure on the tip is spread over a larger surface area.

2. The height of surface 22 can recede from edge 22 c to edge 22 d. Oneprofile would be a wedge/slanted shape with the lower edge trailing(near 22 d) so that pressure is reduced as the tip rolls over the DUTand the elastomers are compressed. The wedge can be in the form of acurved surface, such as convex as shown.

In FIG. 6 it can be seen how tip 12 shown in three position, will engagethe DUT 30 in positions A, B, C (actually continuously) during travel.

FIG. 7 illustrates an end view of the tip.

FIG. 8 illustrate a side view having a curvature 32 of the neck 14showing a gradual thinning of the neck as it reaches the tip andwidening as it reaching the base of the neck, to provide greaterstrength.

A method of manufacturer is also disclosed including any or all of thefollowing steps in any order:

a method of reducing tip pressure between a device under test (DUT) anda test pin in a test housing, the pin having a tip which has a contactsurface comprising:

a. forming the tip of the pin so that it has a curvature on its contactsurfaces, so that when it engages a contact of a DUT, the area ofcontact between the tip and DUT travels along the curved tip surface;

b. forming a widening the tip contact surface from a point of initialcontact with the DUT to a point of final contact with the DUT as it isinserted into the housing, where the tip contact surface is wider towardthe point of final contact.

A method of reducing tip pressure between a device under test (DUT) anda test pin in a test housing, the pin having a tip which has a contactsurface comprising:

a. forming the tip of the pin so that it has a curvature on its contactsurfaces, so that when it engages a contact of a DUT, the area ofcontact between the tip and DUT travels along the curved tip surface;

b. forming a declining tip height along the tip contact surface from apoint of initial contact with the DUT to a point of final contact withthe DUT as it is inserted into the housing, where the tip height islower toward the point of final contact.

Also disclosed is a controlled pressure test pin for use in a test pinhousing on a device under test (DUT) the pin comprising any or all ofthe following elements:

a. a tip formed at an end of the test pin, the tip being configured toengage a contact on the DUT from an initial point where the tip firstengages the DUT to a final point where the DUT is in a test position inthe housing, during which the pin is deflected into the housing,

b. said tip having a top surface configured to engage the DUT, said topsurface being narrower at the point of initial engagement than at saidfinal point, so that pressure between the tip and the DUT will tend tobe more constant instead of rising as tip deflection increases.

A controlled pressure test pin for use in a test pin housing on a deviceunder test (DUT) the pin comprising any or all of the followingelements:

a. a tip formed at an end of the test pin, the tip being configured toengage a contact on the DUT from an initial point where the tip firstengages the DUT to a final point where the DUT is in a test position inthe housing, during which the pin is deflected into the housing,

b. said tip having a top surface configured to engage the DUT, said topsurface being higher at the point of initial engagement than at saidfinal point so that pressure between the tip and the DUT will tend to bemore constant instead of rising as tip deflection increases.

A controlled pressure test pin for use in a test pin housing on a deviceunder test (DUT) the pin comprising any or all of the followingelements:

a. a tip formed at an end of the test pin, the tip being configured toengage a contact on the DUT from an initial point where the tip firstengages the DUT to a final point where the DUT is in a test position inthe housing, during which the pin is deflected into the housing,

b. said tip having a top surface configured to engage the DUT, said topsurface being higher at the point of initial engagement than at saidfinal point so that pressure between the tip and the DUT will tend to bemore constant instead of rising as tip deflection increases; and

c. said tip having a top surface configured to engage the DUT, said topsurface being higher at the point of initial engagement than at saidfinal point so that pressure between the tip and the DUT will tend to bemore constant instead of rising as tip deflection increases.

FIGS. 9 and 10 illustrate the curvature as well. In FIGS. 11-11 a thiscurvature can be seen an undercutting/sculpting away a portion of theneck at its rear sidewalls to thin the neck.

The above description and its applications as set forth herein isillustrative and is not intended to limit the scope of the invention.Variations and modifications of the embodiments disclosed herein arepossible and practical alternatives to and equivalents of the variouselements of the embodiments would be understood to those of ordinaryskill in the art upon study of this patent document. These and othervariations and modifications of the embodiments disclosed herein may bemade without departing from the scope and spirit of the invention.

The invention claimed is:
 1. A method of maintaining constant tippressure between a device under test (DUT) and a test pin in a testhousing as a tip wears from repeated use, the pin having generallyplanar sidewalls and a cross sectional width being the distance betweenthe sidewalls and having a tip extending from a distal end of the pin,the tip having a contact surface, having sidewalls and the contactsurface width being the distance between the sidewalls, comprising: a.forming the tip of the pin so that it has a curvature on its contactsurfaces, so that when it engages a contact of a DUT, the area ofcontact between the tip and DUT travels along the curved tip surface; b.forming the tip so that it has an initial width is a predetermined widthat a point at which the tip contacts the DUT and wherein said tip widthnarrows as the pin worn down by repeated engagement with the DUT; c.forming the tip with a tapered neck portion which narrows from thecontact surface toward the distal end of the pin; so that as the tip isworn away, the width of the tip is narrowed.
 2. A controlled pressuretest pin for use in a test pin housing on a device under test (DUT) thepin comprising: a. a test pin having generally planar sidewalls; b. atip formed at a distal end of the test pin, the tip having tip sidewallsand a distal tip surface, thereby defining a tip width between the tipsidewalls at said distal tip surface, and being configured to engage acontact on the DUT from an initial contact point where the tip firstengages the DUT to a final contact point where the DUT is fully engagedin a test position in the housing, during which the pin is deflectedinto the housing; c. said tip including a neck portion extending fromsaid distal tip surface toward said distal end of said pin, said neckportion having a tapering width from said distal tip surface toward saiddistal end portion, so that as said distal tip surface is worn byrepeated contact with said DUT, said width progressively decrease.
 3. Acontrolled pressure test pin system configured to compensate for pinwear, for use in a test pin housing which receives a device under test(DUT); the pin comprising: a. a tip formed at a distal end of the testpin, the tip being configured to engage a contact on the DUT from aninitial point where the tip first engages the DUT to a final point wherethe DUT is in a test position in the housing, during which the pin isdeflected into the housing against an elastomeric bias force, b. saidtip having a top surface configured to engage the DUT, said top surfacebeing higher in the housing at the point of initial engagement than atsaid final point when deflected by engagement with the DUT; and said tiphaving a top surface configured to engage the DUT, said top surfacehaving a predetermined width, with the tip having a progressivelywidening width as it approaches the test pin distal end, so that whenthe top surface of the pin wears in response to repeated engagement withthe DUT, the width of the top surface will be progressively narrowerthereby increasing the tip pressure to compensate for decreasingelastomeric bias force as the even shorter tip is deflected less as itwears.
 4. The test pin of claim 2 wherein the neck portion includes a. atapered portion from the distal tip surface; b. said tapered portionbeing joined at one end to a portion of spaced apart sidewalls and afixed width; and c. said tapered portion being joined at another end tolower neck portion, which in turn is connected to the distal end of thetest pin, the lower neck portion having a reverse taper which widens tomate with the distal end of the test pin.
 5. The test pin of claim 4wherein said lower neck portion further includes a radiussed recesstherein.